BIOMOLECULES PRACTICAL QUESTIONS
1.
A student performs Benedict’s test on a solution and observes a green precipitate after heating.
Explain what this indicates about the sugar concentration and type present.
2.
A sample gives a negative result with Benedict’s test but turns positive after acid hydrolysis.
Identify the likely sugar present and explain the chemistry behind the observation.
3.
Describe how you would differentiate between glucose and fructose using Seliwanoff’s test and
explain the expected observations.
4.
A food sample produces a blue-black color upon addition of iodine test.
Explain the molecular basis of this color change.
5.
Explain why sucrose does not reduce Benedict’s reagent unless it is first hydrolyzed.
6.
A solution gives a violet color with Biuret test.
Explain what structural feature of proteins leads to this result.
7.
A protein sample fails the Biuret test but gives a positive result with Ninhydrin test.
Interpret these findings.
8.
Describe the principle of the Xanthoproteic test and identify which amino acids would give a
positive result.
9.
A sample turns yellow upon addition of concentrated nitric acid and becomes orange after
alkalization.
Identify the test and explain the reaction mechanism.
,10.
Explain how you would distinguish between primary and secondary amino acids using Ninhydrin
test.
11.
A translucent spot appears on filter paper after applying a sample.
Explain what this indicates and why lipids produce this effect.
12.
Describe the principle and expected result of the Sudan III test.
13.
A sample forms a stable emulsion when mixed with ethanol and water.
Explain what this indicates about the presence of lipids.
14.
Explain the chemical basis of the saponification reaction and its significance in lipid analysis.
15.
A sample gives positive results for both Benedict’s test and Biuret test.
What conclusions can you draw about the sample composition?
16.
Explain how temperature affects enzyme activity in biochemical assays involving biomolecules.
17.
A student overheats a sample during Benedict’s test and obtains an unexpected negative result.
Provide a possible explanation.
18.
Discuss the importance of using controls in biochemical tests for biomolecules.
19.
Describe how pH can influence the outcome of protein-based tests such as the Biuret test.
20.
You are given an unknown solution. Outline a systematic procedure to identify whether it contains
carbohydrates, proteins, or lipids.
,21.
A student is given three unknown solutions (A, B, and C). They accidentally mix a small amount of
solution B into A before performing Benedict’s test on solution A. The result is a brick-red
precipitate, whereas previously solution A alone gave no reaction.
Explain how this contamination affects interpretation and suggest how the student can correct the
experiment.
22.
During a practical, a student performs Biuret test but mistakenly adds excess sodium hydroxide
before adding copper sulfate. A faint blue color persists instead of violet.
Analyze what went wrong chemically and how reagent order influences the result.
23.
A student overheats a sample while performing Benedict’s test, causing the solution to evaporate
partially. After cooling, no precipitate forms.
Discuss how overheating and concentration changes can lead to false results.
24.
Two students test the same solution using iodine test. One observes a blue-black color, while the
other reports no change. It is later discovered that one sample was diluted with distilled water.
Explain the discrepancy and how dilution affects test sensitivity.
25.
A student performs acid hydrolysis on a sugar solution but forgets to neutralize the acid before
conducting Benedict’s test. The result is negative.
Explain why this occurs and the role of pH in the reaction.
26.
An unknown sample gives a positive Biuret test and a weak positive Ninhydrin test. The student
concludes the sample contains only free amino acids.
Critically evaluate this conclusion and provide a more accurate interpretation.
27.
A food sample suspected to contain starch is accidentally contaminated with glucose. The student
performs iodine test and Benedict’s test.
Predict the results and explain how mixed biomolecules complicate identification.
28.
A student uses Sudan III test on a sample containing both lipids and proteins. The student reports
only lipids are present.
Explain why this conclusion may be incomplete and suggest additional confirmatory tests.
, 29.
An unknown solution gives a negative Biuret test but a strong positive Ninhydrin test. However, the
student had heated the sample for a prolonged period before testing.
Explain how heating may influence protein structure and test outcomes.
30.
A student performs Seliwanoff’s test on a sugar solution but observes a delayed faint pink color
instead of rapid cherry-red.
Interpret this result and explain possible causes including contamination or incorrect timing.
31.
A student is required to estimate reducing sugar concentration using Benedict’s test. They
accidentally double the volume of reagent but keep the sample volume constant.
Explain how this affects the intensity of the result and the accuracy of conclusions.
32.
During protein estimation, a student prepares a diluted sample but forgets to account for the dilution
factor in final calculations.
Discuss how this error affects reported protein concentration and how it should be corrected.
33.
A student prepares a standard glucose solution incorrectly (higher concentration than intended) and
uses it as a reference for comparison.
Explain how this affects the interpretation of unknown samples.
34.
A lipid extraction experiment is performed, but the student uses excess ethanol, causing incomplete
phase separation.
Explain how this affects the detection of lipids using emulsion-based tests.
35.
A student uses contaminated test tubes previously used for protein assays when testing for
carbohydrates using Benedict’s test.
Discuss how this could affect results and lead to false conclusions.
36.
During a practical, a student forgets to include a negative control while performing Biuret test.
Explain why this is a critical error in experimental design.
1.
A student performs Benedict’s test on a solution and observes a green precipitate after heating.
Explain what this indicates about the sugar concentration and type present.
2.
A sample gives a negative result with Benedict’s test but turns positive after acid hydrolysis.
Identify the likely sugar present and explain the chemistry behind the observation.
3.
Describe how you would differentiate between glucose and fructose using Seliwanoff’s test and
explain the expected observations.
4.
A food sample produces a blue-black color upon addition of iodine test.
Explain the molecular basis of this color change.
5.
Explain why sucrose does not reduce Benedict’s reagent unless it is first hydrolyzed.
6.
A solution gives a violet color with Biuret test.
Explain what structural feature of proteins leads to this result.
7.
A protein sample fails the Biuret test but gives a positive result with Ninhydrin test.
Interpret these findings.
8.
Describe the principle of the Xanthoproteic test and identify which amino acids would give a
positive result.
9.
A sample turns yellow upon addition of concentrated nitric acid and becomes orange after
alkalization.
Identify the test and explain the reaction mechanism.
,10.
Explain how you would distinguish between primary and secondary amino acids using Ninhydrin
test.
11.
A translucent spot appears on filter paper after applying a sample.
Explain what this indicates and why lipids produce this effect.
12.
Describe the principle and expected result of the Sudan III test.
13.
A sample forms a stable emulsion when mixed with ethanol and water.
Explain what this indicates about the presence of lipids.
14.
Explain the chemical basis of the saponification reaction and its significance in lipid analysis.
15.
A sample gives positive results for both Benedict’s test and Biuret test.
What conclusions can you draw about the sample composition?
16.
Explain how temperature affects enzyme activity in biochemical assays involving biomolecules.
17.
A student overheats a sample during Benedict’s test and obtains an unexpected negative result.
Provide a possible explanation.
18.
Discuss the importance of using controls in biochemical tests for biomolecules.
19.
Describe how pH can influence the outcome of protein-based tests such as the Biuret test.
20.
You are given an unknown solution. Outline a systematic procedure to identify whether it contains
carbohydrates, proteins, or lipids.
,21.
A student is given three unknown solutions (A, B, and C). They accidentally mix a small amount of
solution B into A before performing Benedict’s test on solution A. The result is a brick-red
precipitate, whereas previously solution A alone gave no reaction.
Explain how this contamination affects interpretation and suggest how the student can correct the
experiment.
22.
During a practical, a student performs Biuret test but mistakenly adds excess sodium hydroxide
before adding copper sulfate. A faint blue color persists instead of violet.
Analyze what went wrong chemically and how reagent order influences the result.
23.
A student overheats a sample while performing Benedict’s test, causing the solution to evaporate
partially. After cooling, no precipitate forms.
Discuss how overheating and concentration changes can lead to false results.
24.
Two students test the same solution using iodine test. One observes a blue-black color, while the
other reports no change. It is later discovered that one sample was diluted with distilled water.
Explain the discrepancy and how dilution affects test sensitivity.
25.
A student performs acid hydrolysis on a sugar solution but forgets to neutralize the acid before
conducting Benedict’s test. The result is negative.
Explain why this occurs and the role of pH in the reaction.
26.
An unknown sample gives a positive Biuret test and a weak positive Ninhydrin test. The student
concludes the sample contains only free amino acids.
Critically evaluate this conclusion and provide a more accurate interpretation.
27.
A food sample suspected to contain starch is accidentally contaminated with glucose. The student
performs iodine test and Benedict’s test.
Predict the results and explain how mixed biomolecules complicate identification.
28.
A student uses Sudan III test on a sample containing both lipids and proteins. The student reports
only lipids are present.
Explain why this conclusion may be incomplete and suggest additional confirmatory tests.
, 29.
An unknown solution gives a negative Biuret test but a strong positive Ninhydrin test. However, the
student had heated the sample for a prolonged period before testing.
Explain how heating may influence protein structure and test outcomes.
30.
A student performs Seliwanoff’s test on a sugar solution but observes a delayed faint pink color
instead of rapid cherry-red.
Interpret this result and explain possible causes including contamination or incorrect timing.
31.
A student is required to estimate reducing sugar concentration using Benedict’s test. They
accidentally double the volume of reagent but keep the sample volume constant.
Explain how this affects the intensity of the result and the accuracy of conclusions.
32.
During protein estimation, a student prepares a diluted sample but forgets to account for the dilution
factor in final calculations.
Discuss how this error affects reported protein concentration and how it should be corrected.
33.
A student prepares a standard glucose solution incorrectly (higher concentration than intended) and
uses it as a reference for comparison.
Explain how this affects the interpretation of unknown samples.
34.
A lipid extraction experiment is performed, but the student uses excess ethanol, causing incomplete
phase separation.
Explain how this affects the detection of lipids using emulsion-based tests.
35.
A student uses contaminated test tubes previously used for protein assays when testing for
carbohydrates using Benedict’s test.
Discuss how this could affect results and lead to false conclusions.
36.
During a practical, a student forgets to include a negative control while performing Biuret test.
Explain why this is a critical error in experimental design.
